Processes for producing dihydric phenols, e.g., catechol and hydroquinone, by hydroxylation of phenols include so-called ketone peroxide processes comprising reacting a phenol with a ketone peroxide in the presence of a sulfuric acid catalyst which are known to attain the highest yield (see U.S. Pat. Nos. 4,078,006).
Any of the known ketone peroxide processes, however, is still unsatisfactory in view of the yield and ease of isolation of the product. For example, use a large quantity of a sulfate as a catalyst in these processes not only makes it difficult to separate the catalyst from the product but requires a neutralization step. If the amount of the sulfate to be used is reduced, the yield of the product decreases. When in using sulfuric acid as a catalyst, the yield reached is low regardless of its amount, and a neutralization step is still needed.